Pass Labs (Vertical Bi-amp)

[Trn335]

Some background: over my 25 years of ML SL3 ownership I've had numerous configurations in several systems; amps, preamps, speakers, sources, etc. I rebuilt the SL3's a few years ago (new panels and caps) even though I used them only infrequently my systems but, I know they can sound really good in the right setting. Last year I had a new house built with a large, open area (18x40x10) and thought this might be a good situation to bring the SL3's bout of semi-retirement as I now had the space to play with them in the room.

Upon moving in to the new place, I set up the system with a modded Oppo BDP105D, a custom turntable, and a Primaluna Dialogue Integrated with phono pre. I listened to this setup for 4-5 months or so. But it wasn't really 'it' - lots of re-positioning, room treatments, experimentation - not bad but not great. I recalled a configuration from many years ago where I drove the SL3's with a Pass Labs X150 direct from a Wadia CDP and I remembered it as really engaging. I no longer had the Wadia but the Oppo can also act as a pre so I pulled the Pass out of my studio system and replaced the Primaluna. The effect was immediately noticeable and the improvement felt to me as mostly power-related, better dynamics, fuller across the spectrum. The Primaluna had sounded like it was working hard to drive the speakers enough to fill the room whereas the Pass didn't seem to strain. But, I kinda like tubes.

This led me to pick up a Schiit Freya+ pre as it would allow me to get tubes in the signal path (or not, because the Freya can operate in three modes: passive, SS buffered, or tube; it gave me options). Aside: oddly enough, I've found I prefer passive mode on the Freya and have listened to it that way exclusively. I added a Schiit Urd transport and Benchmark Dac3 and removed the Oppo from the system. Not any great change here, neither better nor worse, just one more component to turn on, mostly. Not really surprising as the Oppo is a pretty good implementation of a delta-sigma dac, like the Benchmark.

Over the years, I've driven the SL3's with all manner of amps; Krell, Levinson, Acurus, Carver/Sunfire, Yamaha, and others I can't recall. But, if you have tried a Pass amp driving e-stats, you probably already know there seems to be some synergy there. I don't know why, there just is. Which is why I still have the Pass and all the other amps are long gone. And that brings me to the point of this post (finally, you might rightfully say).

About two months ago, I came across another Pass X150 at an attractive price. I thought, what the heck. It's a great-sounding amp and you can never have too many great-sounding amps, right? As the post title says, I decided to try vertically bi-amping the SL3's with the pair of Pass amps (does that make them 'stereoblocks'?) My reasoning for vertical instead of horizontal was to keep cable runs as short as possible.

I did not expect the results. What the...?!? Stunning. I mean, an instant, jaw-dropping difference. More. Of everything. Detail, air, authority, finesse, soundstage, presence, scale, realism, yada, yada, all the buzzwords...wow, a 'live' performance in the living room. For example, I had a pair of Rythmik L12 subs supplementing the speakers previously - I had to tune them out, essentially. They're basically plant stands now.

I'm an engineer (and musician). The engineer wants badly to understand what happened here. The musician is in revelry.

 

[Russr]

Thanks for the interesting post.
Forgive the ignorance - by "Vertical Bi-amping" do you mean 1 "stereo block" is handling the panels of both (L AND R) channels, and the other amp is handling the bass, or do you mean that one "stereo-block" amp is using one channel for the panel and the other channel for the bass on the same speaker (one steroblock for L, one for R)?

Thanks

 

[Trn335]

Thanks for the interesting post.
Forgive the ignorance - by "Vertical Bi-amping" do you mean 1 "stereo block" is handling the panels of both (L AND R) channels, and the other amp is handling the bass, or do you mean that one "stereo-block" amp is using one channel for the panel and the other channel for the bass on the same speaker (one steroblock for L, one for R)?

Thanks

Yes, vertical bi-amping is one amp per speaker wherein one channel of the amp drives the bass cab and the other drives the panel. The more common method of horizontal bi-amping is one amp driving panels (L&R) and another amp driving bass bins. To do vertical, you really need two identical amps so that the 'behavior' is the same per channel, L&R. Whereas with horizontal bi-amping you could use, say, a tube amp running the panels (L&R) and a SS amp for the bass bins.

I theorize that the resulting improvement from vertical bi-amping could be three things; shorter cable runs, better channel separation, and an abundance of power. Admittedly, I have a hard time believing there is an audible difference between a 2m long speaker cable and a pair of 1/2m cables. Likewise, it's hard for me to make an argument that channel separation would make much difference in a well-designed stereo amp such as Pass Labs. But, then again, you can't argue that one way to ensure channels are ultimately separated is to use completely separate amps for each channel. As for power, you'd think 300w/channel (@4ohms) from a single amp would be sufficient to get excellent performance from these speakers as this is well up in the recommended range of 20-400w@4ohms nominal per ML. However, going from 300w/channel to 600w/channel does mean going from a shortfall of 25% to a headroom of 50% at max recommended speaker power.

In any case, some one or a combination of these factors (maybe others - though I can't think of what they might be) made a clearly audible difference (in my room) in an already high-performing system.

 

[Jazzman53]

I'm not surprised that you noticed the difference vertical bi-amping can make. Does it seem more dynamic and alive? I think so.

I've been vertical bi-amping my DIY hybrid ESLs since 2008, and I wouldn't do it any other way.

The theory goes something like this:

Generally; it takes more power, moving more air, to make bass than it does to make mids/treble. So; horizontal bi-amping under-utilizes the mid/treble channels and over-utilizes the bass channels.

The difference is perhaps not so clear cut in an ESL, but it's still assumed that bass needs more power. Either way; we want to utilize all available power, and waste none of it.

I've read that Pass amps are Class A (not push/pull) so their power supply may be configured differently, but most stereo amps have a common power supply that both channels draw from.

It follows that power not drawn by one channel is then available to be drawn by the other channel. Hence; in this case vertical bi-amping better utilizes the available power.

 

[Trn335]

I'm not surprised that you noticed the difference vertical bi-amping can make. Does it seem more dynamic and alive? I think so.

I've been vertical bi-amping my DIY hybrid ESLs since 2008, and I wouldn't do it any other way.

The theory goes something like this:

Generally; it takes more power, moving more air, to make bass than it does to make mids/treble. So; horizontal bi-amping under-utilizes the mid/treble channels and over-utilizes the bass channels.

The difference is perhaps not so clear cut in an ESL, but it's still assumed that bass needs more power. Either way; we want to utilize all available power, and waste none of it.

I've read that Pass amps are Class A (not push/pull) so their power supply may be configured differently, but most stereo amps have a common power supply that both channels draw from.

It follows that power not drawn by one channel is then available to be drawn by the other channel. Hence; in this case vertical bi-amping better utilizes the available power.

The total power of a stereo amp is not available to a single channel unless it's bridge-able by design. The Pass X-series amps are not bridge-able (and run Class A at lower wattage, then Class AB above). The available power of the Pass Labs X150 is 150W/channel@8ohms, 300W@4ohms.

The math says that an identical pair of 300W/channel stereo amps will have the same amount of power available to a given channel/load whether vertically or horizontally bi-amped. The only difference should be in channel separation (and length of cables, possibly.)

Given this, I suspect there are one or more other things going on here with bi-amping a hybrid speaker system such as these, whether vertical or horizontal.

One, by bi-amping, you're connecting directly to the specific crossover network of the drivers, not jumpered to a single connection. Does this change the characteristics of the load to an amp? I think the answer is, certainly.

Two, given the recognized 'oddness' of the panel load vs the bass bin, does this cause the amp to behave differently? For example, what if one side of the amp is seeing a nominal 8ohm load and needing higher current and the other side is seeing 1ohm and more voltage in vertical config as opposed to each amp seeing essentially the same type of specific load L to R (high current on one amp, high voltage on the other) in a horizontal config? Do you potentially use more of the amp's capabilities in one config over the other?

I think there might be an argument to be made here when you factor in musical content and the relative power levels required to produce certain frequency ranges and the type of transducers/loads producing them. I could see, for example, that in a horizontal bi-amp config the amp dedicated to panels might be 'loafing' compared to the amp covering the cone transducers. Whereas in vertical config, the amp has to produce full range.

Just a theory.